CS Prelim 1 Review Fall 2017

Transcription

1 CS 1110 Prelim 1 Review Fall 2017

2 Exam Info Prelim 1: 7:30 9:00PM, Thursday, October 12th Last name A J in Uris G01 Last name K Z in Statler Auditorium SDS Students will get an To help you study: Study guides, review slides are online Solutions to Assignment 2 are in CMS Arrive early! Helps reducing stress 10/11/17 Prelim 1 Review 2

3 Grading We will announce approximate letter grades We adjust letter grades based on all exams But no hard guidelines (e.g. mean = grade X) May adjust borderline grades again at final grades Use this to determine whether you want to drop Drop deadline is next week, October 17 th Goal: Have everyone graded by end of Saturday Will definitely notify you if you made less than C 10/11/17 Prelim 1 Review 3

4 What is on the Exam? Five Questions out of Six Topics: String slicing functions (A1) Call frames and the call stack (A2) Functions on mutable objects (A3) Testing and debugging (Lab 3 & 6, Lec. 11) Lists and For-Loops (Lab 7) Short Answer (Terminology) + 2 pts for writing your name and net-id 10/11/17 Prelim 1 Review 4

5 What is on the Exam? String slicing functions (A1) Will be given a function specification Implement it using string methods, slicing Call frames and the call stack (A2) Functions on mutable objects (A3) Testing and debugging (Lab 3 & 6, Lecture 11) Lists and For-Loops (Lab 7) Short Answer (Terminology) 10/11/17 Prelim 1 Review 5

6 String Slicing def make_netid(name,n): """Returns: a netid for name with suffix n Netid is either two letters and a number (if the student has no middle name) or three letters and a number (if the student has a middle name). Letters in netid are lowercase. Example: make_netid('walker McMillan White',2) is 'wmw2' Example: make_netid('walker White',4) is 'ww4' Parameter name: the student name Precondition: name is a string either with format '<first-name> <last-name>' or '<first-name> <middle-name> <last-name>' Parameter n: the netid suffix Precondition: n > 0 is an int.""" 10/11/17 Prelim 1 Review 6

7 Useful String Methods Method s.find(s1) s.rfind(s1) s.lower() s.upper() Result Returns first position of s1 in s; -1 if not there. Returns LAST position of s1 in s; -1 if not there. Returns copy of s with all letters lower case Returns copy of s with all letters upper case We will give you any methods you need But you must know how to slice strings! 10/11/17 Prelim 1 Review 7

8 What is on the Exam? String slicing functions (A1) Call frames and the call stack (A2) Very similar to A2 (see solution in CMS) May have to draw a full call stack See lectures 4 and 9 (slide typos corrected) Functions on mutable objects (A3) Testing and debugging (Lab 3 & 6, Lecture 11) Lists and For-Loops (Lab 7) Short Answer (Terminology) 10/11/17 Prelim 1 Review 8

9 Call Stack Example Given functions to right Function fname() is not important for problem Use the numbers given Execute the call: lname_first('john Doe') Draw entire call stack when helper function lname completes line 1 Draw nothing else def lname_first(s): """Precondition: s in the form <first-name> <last-name>""" first = fname(s) last = lname(s) return last + ',' + first def lname(s): """Prec: see last_name_first""" end = s.find(' ') return s[end+1:] 10/11/17 Prelim 1 Review 9

10 Example with a Mutable Object def cycle_left(p): """Cycle coords left Precondition: p a point""" temp = p.x p.x = p.y p.y = p.z p.z = temp May get a function on a mutable object >>> p = Point3(1.0,2.0,3.0) >>> cycle_left(p) You are not expected to come up w/ the folder Will provide it for you You just track changes Diagram all steps 10/11/17 Prelim 1 Review 10

11 Example with a Mutable Object def cycle_left(p): id1 p id1 1 2 """Cycle coords left Precondition: p a point""" temp = p.x p.x = p.y x y z Point3 3 p.y = p.z 4 p.z = temp >>> p = Point3(1.0,2.0,3.0) >>> cycle_left(p) Function Call 10/11/17 Prelim 1 Review 11

12 What is on the Exam? String slicing functions (A1) Call frames and the call stack (A2) Functions on mutable objects (A3) Given an object type (e.g. class) Attributes will have invariants Write a function respecting invariants Testing and debugging (Lab 3 & 6, Lecture 11) Lists and For-Loops (Lab 7) Short Answer (Terminology) 10/11/17 Prelim 1 Review 12

13 Class: RGB Example from Assignment 3 Constructor function: RGB(r,g,b) Remember constructor is just a function that gives us back a mutable object of that type Attributes: Attribute Invariant red int, within range green int, within range blue int, within range /11/17 Prelim 1 Review 13

14 Function that Modifies Object def lighten(rgb): """Lighten each attribute by 10% Attributes get lighter when they increase. Parameter rgb: the color to lighten Precondition: rgb an RGB object""" pass # implement me 10/11/17 Prelim 1 Review 14

15 Class: Length Another Example Constructor function: Length(ft,in) Remember constructor is just a function that gives us back a mutable object of that type Attributes: Attribute feet Invariant int, non-negative, = 12 in inches int, within range /11/17 Prelim 1 Review 15

16 Function that Does Not Modify Object def difference(len1,len2): """Returns: Difference between len1 and len2 Result is returned in inches Parameter len1: the first length Precondition: len1 is a length object longer than len2 Parameter len2: the second length Precondition: len2 is a length object shorter than len1""" pass # implement me 10/11/17 Prelim 1 Review 16

17 What is on the Exam? String slicing functions (A1) Call frames and the call stack (A2) Functions on mutable objects (A3) Testing and debugging (Lab 3 & 6, Lecture 11) Coming up with test cases Tracing program flow Understanding assert statements Lists and For-Loops (Lab 7) Short Answer (Terminology) 10/11/17 Prelim 1 Review 17

18 def pigify(w): Picking Test Cases """Returns: copy of w converted to Pig Latin 'y' is a vowel if it is not the first letter If word begins with a vowel, append 'hay' If word starts with 'q', assume followed by 'u'; move 'qu' to the end, and append 'ay' If word begins with a consonant, move all consonants up to first vowel to end and add 'ay' Parameter w: the word to translate Precondition: w contains only (lowercase) letters""" 10/11/17 Prelim 1 Review 18

19 Debugging Example def replace_first(word,a,b): """Returns: a copy with FIRST instance of a replaced by b Example: replace_first('crane','a','o') returns 'crone' Example: replace_first('poll','l','o') returns 'pool' Parameter word: The string to copy and replace Precondition: word is a string Parameter a: The substring to find in word Precondition: a is a valid substring of word Parameter b: The substring to use in place of a Precondition: b is a string""" 10/11/17 Prelim 1 Review 19

20 Debugging Example def replace_first(word,a,b): """Returns: a copy with FIRST a replaced by b""" pos = word.rfind(a) print(pos) before = word[:pos] print(before) after = word[pos+1:] print(after) result = before+b+after print(result) return result >>> replace_first('poll', 'l', 'o') 3 pol polo 'polo' >>> replace_first('askew', 'sk', 'ch') 1 a kew achkew 'achkew' Identify the bug(s) in this function. 10/11/17 Prelim 1 Review 20

21 What is on the Exam? String slicing functions (A1) Call frames and the call stack (A2) Functions on mutable objects (A3) Testing and debugging (Lab 3 & 6, Lecture 11) Lists and For-Loops (Lab 7) Given a function specification Implement it using a for-loop Challenge is how to use accumulators Short Answer (Terminology) 10/11/17 Prelim 1 Review 21

22 Useful List Methods Method Result x.index(a) Returns first position of a in x; error if not there x.append(a) Modify x to add element a to the end x.insert(a,k) Modify x to put a at position k (and move rest to right) x.remove(a) Modify x to remove first occurrence of a x.sort() Modify x so that elements are in sorted order We will give you any methods you need But you must know how to slice lists! 10/11/17 Prelim 1 Review 22

23 For-Loop in a Fruitful Function def replace(thelist,a,b): """Returns: COPY of thelist with all occurrences of a replaced by b Example: replace([1,2,3,1], 1, 4) = [4,2,3,4]. Parameter thelist: list to copy Precondition: thelist is a list of ints Parameter a: the value to remove Precondition: a is an int Parameter b: the value to insert Precondition: b is an int """ return [] # Stub return. IMPLEMENT ME 10/11/17 Prelim 1 Review 23

24 For-Loop in a Procedure def pairswap(seq): """MODIFIES thelist, swapping each two elements with each other Example: if a = [0,2,4,5], pairswap(a) makes a into [2,0,5,4] if a = [1,2], pairswap(a) turns a into [2,1] Parameter thelist: list to modify Precondition: thelist is a list with an even number of elements.""" pass # implement me 10/11/17 Prelim 1 Review 24

25 What is on the Exam? String slicing functions (A1) Call frames and the call stack (A2) Functions on mutable objects (A3) Testing and debugging (Lab 3 & 6, Lecture 10) Lists and For-Loops (Lab 7) Short Answer (Terminology) See the study guide Look at the lecture slides Read relevant book chapters In that order 10/11/17 Prelim 1 Review 25

26 Good Luck! 10/11/17 Prelim 1 Review 26